The present invention relates to a vehicle brake controller that controls a brake pump of a vehicle. The present invention further relates to a vehicle brake control method.
Some types of vehicle brake apparatuses generate brake fluid pressure in each of wheel cylinders provided in wheels so that braking force is applied to each wheel. Specifically, a brake apparatus that performs anti-lock brake control (ABS control) ensures steerability of a vehicle by suppressing locking of the wheels when the vehicle is braked quickly. In the ABS control, the brake controller controls the brake apparatus in such a manner that a fluctuation cycle of brake fluid pressure of each wheel cylinder is repeated. The fluctuation cycle of the fluid pressure includes decreasing, keeping, and increasing of the brake fluid pressure.
A brake controller described in Japanese National Phase Laid-Open Patent Publication No. 2001-505505 introduces excessive brake fluid that has been sent from a wheel cylinder to a reservoir when the brake fluid pressure in the wheel cylinder is to be decreased. The brake controller then sucks the brake fluid from the reservoir to the exterior by means of a pump. The brake controller estimates the increase amount of the brake fluid in the reservoir from when the brake fluid pressure in the wheel cylinder starts to decrease to when the brake fluid pressure starts to be maintained at a constant level. The brake controller adjusts the rotational speed of a motor, which is the drive source of the pump, in such a manner as to suck the brake fluid from the reservoir by the amount corresponding to the increase amount before the subsequent cycle is started. This prevents the reservoir from becoming full with the excessive brake fluid during the ABS control.
However, the duration of the fluctuation cycle of the fluid pressure varies from one cycle to another. In other words, the rotational speed of the motor is changed at different timings from one fluctuation cycle of the brake fluid to another. Thus, in the ABS control, the rotational speed of the motor changes non-periodically, leading to non-periodic change in at least one of the noise caused by the pump and the noise brought about by the motor. This may cause discomfort for occupants of the vehicle.
Generally, as the μ value, or the friction coefficient, of a road surface on which the vehicle travels becomes greater, the amount of excessive brake fluid in the ABS control becomes greater. Thus, a brake controller described in Japanese Laid-Open Patent Publication No. 2004-352163 sets the rotational speed of the motor in correspondence with the μ value so that the rotational speed of the motor is changed less frequently during the ABS control. However, if, for example, the μ value changes, the amount of the brake fluid sent from the reservoir may become insufficient.